DESCRIPTION

pcap provides a high level interface to packet capture systems. All pack-
ets on the network, even those destined for other hosts, are accessible
through this mechanism.

ROUTINES

Note:errbuf in pcap_open_live(), pcap_open_offline(),
pcap_findalldevs(), pcap_lookupdev(), and pcap_lookupnet() is assumed to
be able to hold at least PCAP_ERRBUF_SIZE chars.
pcap_open_live() is used to obtain a packet capture descriptor to look at
packets on the network. device is a string that specifies the network
device to open. snaplen specifies the maximum number of bytes to capture.
promisc specifies if the interface is to be put into promiscuous mode.
(Note that even if this parameter is false, the interface could well be
in promiscuous mode for some other reason.) to_ms specifies the read
timeout in milliseconds. errbuf is used to return error text and is only
set when pcap_open_live() fails and returns NULL.
pcap_open_offline() is called to open a "savefile" for reading. fname
specifies the name of the file to open. The file has the same format as
those used by tcpdump(8). The name '-' is a synonym for stdin. errbuf is
used to return error text and is only set when pcap_open_offline() fails
and returns NULL.
pcap_dump_open() is called to open a "savefile" for writing. The name '-'
is a synonym for stdin. NULL is returned on failure. p is a pcap struct
as returned by pcap_open_offline() or pcap_open_live(). fname specifies
the name of the file to open. If NULL is returned, pcap_geterr() can be
used to get the error text.
pcap_dump_fopen() allows the use of savefile functions on the already-
opened stream "f".
pcap_lookupdev() returns a pointer to a network device suitable for use
with pcap_open_live() and pcap_lookupnet(). If there is an error, NULL is
returned and errbuf is filled in with an appropriate error message.
pcap_lookupnet() is used to determine the network number and mask associ-
ated with the network device device. Both netp and maskp are bpf_u_int32
pointers. A return of -1 indicates an error in which case errbuf is
filled in with an appropriate error message.
pcap_dispatch() is used to collect and process packets. cnt specifies the
maximum number of packets to process before returning. A cnt of -1
processes all the packets received in one buffer. A cnt of 0 processes
all packets until an error occurs, EOF is reached, or the read times out
(when doing live reads and a non-zero read timeout is specified).
callback specifies a routine to be called with three arguments: a u_char
pointer which is passed in from pcap_dispatch(), a pointer to the
pcap_pkthdr struct (which precede the actual network headers and data),
and a u_char pointer to the packet data. The number of packets read is
returned. Zero is returned when EOF is reached in a savefile. A return of
-1 indicates an error in which case pcap_perror() or pcap_geterr() may be
used to display the error text.
pcap_dump() outputs a packet to the savefile opened with
pcap_dump_open(). Note that its calling arguments are suitable for use
with pcap_dispatch().
pcap_inject() uses write(2) to inject a raw packet through the network
interface. It returns the number of bytes written or -1 on failure.
pcap_sendpacket() is an alternate interface for packet injection (provid-
ed for compatibility). It returns 0 on success or -1 on failure.
pcap_compile() is used to compile the string str into a filter program.
fp is a pointer to a bpf_program struct and is filled in by
pcap_compile(). optimize controls whether optimization on the resulting
code is performed. netmask specifies the netmask of the local net.
pcap_setfilter() is used to specify a filter program. fp is a pointer to
an array of bpf_program struct, usually the result of a call to
pcap_compile(). -1 is returned on failure; 0 is returned on success.
pcap_freecode() is used to free up allocated memory pointed to by a
bpf_program struct generated by pcap_compile() when that BPF program is
no longer needed, for example after it has been made the filter program
for a pcap structure by a call to pcap_setfilter().
pcap_loop() is similar to pcap_dispatch() except it keeps reading packets
until cnt packets are processed or an error occurs. It does not return
when live read timeouts occur. Rather, specifying a non-zero read timeout
to pcap_open_live() and then calling pcap_dispatch() allows the reception
and processing of any packets that arrive when the timeout occurs. A
negative cnt causes pcap_loop() to loop forever (or at least until an er-
ror occurs). pcap_loop() may be terminated early through an explicit call
to pcap_breakloop(). In this case, the return value of pcap_loop() will
be -2.
pcap_next() returns a u_char pointer to the next packet.
pcap_next_ex() reads the next packet and returns a success/failure indi-
cation: a return value of 1 indicates success, 0 means that the timeout
was exceeded on a live capture, -1 indicates that an error occurred
whilst reading the packet and -2 is returned when there are no more pack-
ets to read in a savefile.
pcap_datalink() returns the link layer type, e.g., DLT_EN10MB.
pcap_snapshot() returns the snapshot length specified when
pcap_open_live() was called.
pcap_is_swapped() returns true if the current savefile uses a different
byte order than the current system.
pcap_major_version() returns the major number of the version of the pcap
used to write the savefile.
pcap_minor_version() returns the minor number of the version of the pcap
used to write the savefile.
pcap_file() returns the stream associated with the savefile.
pcap_stats() returns 0 and fills in a pcap_stat struct. The values
represent packet statistics from the start of the run to the time of the
call. If there is an error or the underlying packet capture doesn't sup-
port packet statistics, -1 is returned and the error text can be obtained
with pcap_perror() or pcap_geterr().
pcap_fileno() and pcap_get_selectable_fd() return the file descriptor
number of the savefile.
pcap_perror() prints the text of the last pcap library error on stderr,
prefixed by prefix.
pcap_geterr() returns the error text pertaining to the last pcap library
error.
pcap_strerror() is provided in case strerror(3) isn't available.
pcap_close() closes the files associated with p and deallocates
resources.
pcap_dump_file() returns the stream associated with a savefile.
pcap_dump_ftell() returns the current file offset within a savefile.
pcap_dump_flush() ensures that any buffered data has been written to a
savefile.
pcap_dump_close() closes the savefile.
pcap_findalldevs() constructs a linked list of network devices that are
suitable for opening with pcap_open_live().
pcap_freealldevs() frees a list of interfaces built by
pcap_findalldevs().
pcap_getnonblock() returns 1 if the capture file descriptor is in non-
blocking mode, 0 if it is in blocking mode, or -1 on error.
pcap_setnonblock() sets or resets non-blocking mode on a capture file
descriptor.
pcap_set_datalink() sets the datalink type on a live capture device that
supports multiple datalink types.
pcap_setdirection() is used to limit the direction that packets must be
flowing in order to be captured.
pcap_list_datalinks() returns an array of the supported datalink types
for an opened live capture device as a -1 terminated array. It is the
caller's responsibility to free this list.
pcap_breakloop() safely breaks out of a pcap_loop(). This function sets
an internal flag and is safe to be called from inside a signal handler.
pcap_open_dead() is used for creating a pcap_t structure to use when cal-
ling the other functions in libpcap. It is typically used when just using
libpcap for compiling BPF code.
pcap_fopen_offline() may be used to read dumped data from an existing
open stream "fp".
pcap_lib_version() returns a string describing the version of libpcap.
pcap_datalink_val_to_name() and pcap_datalink_val_to_description() look
up the name or description of a datalink type by number. These functions
return NULL if the specified datalink type is not known.
pcap_datalink_name_to_val() finds the datalink number for a given da-
talink name. Returns -1 if the name is not known.